confusing schematic symbol, need help

[pine]

I'm looking at a schematic (aa964) for a Princeton Silverface amp, and attached to pin 4 of the rectifier tube is what looks like a capacitor with this notation: +25 --||-- -50 with the POSITIVE side going to ground. On the layout diagram it say +50 on one side and -25 on the other side of the cap, again with the positive side going to ground. I can't read what's on the actual cap, so I need to know

a) what is the value of the cap, 25 or 50 uF, what do I ask for when ordering a new one?

b)which is the correct way to wire it ?

Thanks in advance for your help

[Alex R]

That's a filter cap, 20uF 450v, with the negative side to ground and the positive to the rectifier. Like the other 20uF caps you'll find it under the 'doghouse' above the chassis, not on the rectifier tabs but wired to them with a wire passing through the chassis. Modern value for these is 22uF. For that particular cap 33uF or 47uf would be ok too, with some minor effects on sound (higher values = a bit more punch, less sag)

[Bruce / Mission Amps]

That is a multi section FP type cap where all three capacitors are installed in one canister and share a single ground point, the canister itself.

http://www.tubesandmore.com/scripts/...m=C-EC40-20-20

[Enzo]

Oh, I see what you mean.

Alex, Bruce, he is looking at the bias filter. The bias comes off pin 4 of the tube, though the schematic shows pin 6, not that that matters. And the cap does not connect to pin 4, there is a diode there and a 100k resistor.

You are looking at two things at once.

it is an electrolytic cap, so it has polarity. Note that all the electrolytic caps have a + and - sign by them. Most drawings only put the + sign on one end, since the other end obviously must be the - then. Look at the cathode cap on the input stage up by the input jacks. See the + and - on the left side and the 25 25 on the right?

On any cap, the two values we are most concerned with are capacitance and voltage rating. By all the electrolytic caps you will see these values. Capacitance first, then voltage. it is understood what units these are in, so instead of 25uf (microfarad) at 50 volts, it just says 25-50. Just as the high voltage filters say 20-450, meaning 20uf at 450 volts.

The cap you pointed out is the filter for the bias supply. The bias supply is a negative voltage supply, so the filters have to be wired with their positive ends (+) to ground. The cap doesn't really say -25 +50 by it. What you are seeing it the + and - signs next to the cap itself to indicate which way it is wired. The 25 and 50 are nearby but separate. If you look close, there is a little dash after the 25, since it intends you to read it as 25-50. I usually use a slash myself. I'd write 25/50. That to me removes the possibility of confusing a dash for a minus sign. In any case first number is capacitance, and second number is voltage.

And me personally, I'd prefer to use a 100v cap there instead of the 50. or at the very least a 63v cap.

SO to get a new one, you want a 25uf cap at at least 50 volts. Install it with the + end to ground.

[Alex R]

Yes, must be the bias cap with the 25/50 values he mentioned.

Bruce is right about the multisection cap, forget my stuff about the doghouse, too lazy to look at the layout diagram. Anyhow you weren't talking about that!

[Bruce / Mission Amps]

Yeah the comment about the + end being grounded should have been a big flag for me. sorry.
However... here is what he said:

"and attached to pin 4 of the rectifier tube is what looks like a capacitor with this notation: +25 --||-- -50 with the POSITIVE side going to ground."

You would NEVER connect the bias filter cap to lug/pin 4 of the rectifier tube... for that matter you would never connect any filter cap to lug/pin 4 or 6 of the rectifier,
so that statement threw me off.
I can see where he has the --||-- confused with the use of a schematic drawing of the 25uF/50v cap in the layout....

[Enzo]

SOmetimes I get it right, someone tell my wife that for me.

[pine]

Thank you, guys, I couldn't get on the forum for awhile to read your responses, but that clears it up, and I was looking at a layout diagram, not the schematic, and it appeared that the cap was coming off pin 4 (after the resistor and the diode)

[pine]

By the way, Bruce, I bought a 5E3 kit from you about 3 years ago and I still get compliments on the tone. It's a great amp.